1. Field of the Invention
This invention relates to silver-copper-indium brazing alloys. More particularly it relates to silver-copper-indium brazing alloys in the form of a ductile thin brazing foil that can contain up to about 18 atomic percent of indium.
2. Prior Art
Alloys in the system Ag-Cu-In are used for vacuum tube brazing where high vapor pressure elements cannot be tolerated. The Ag-Cu-In alloys used currently are restricted to a maximum indium content of 15 weight percent. Above about 12 weight percent of indium, the alloys are difficult to fabricate by conventional casting and rolling technique. Therefore, the use of Ag-Cu-In alloys for brazing foil produced by prior methods is limited to alloys containing a maximum of about 12 percent by weight.
An alloy with 15 percent by weight In and a Ag-Cu eutectic ratio has a liquidus temperature of 705.degree. C. and a melting range of 75.degree. C. This wide melting range causes the alloy to liquate during the brazing cycle. Also the 15 percent by weight In, Ag-Cu eutectic ratio composition is the lowest melting of all the Ag base low vapor pressure brazing alloys available as foil, and there is a need for brazing alloys with a lower liquidus temperature.
U.S. Pat. No. 3,856,513 discloses a wire product where alloys are represented by the formula TiXj wherein T is a transition metal or mixture thereof and X is Al, Sb, Be, B, Ge, C, In, P, Si or Sn or mixtures thereof. The transition metals include metals from Groups IB, IIIB, IVB, VB, VIB, VIIB and VIIIB of the periodic table, i is from about 70 to about 87 and j is from about 13 to about 30 atomic percent. The patent also teaches that the alloys contain at least 50 percent amorphous phase. As is apparent from that description, 280 binary alloys and an infinite number of tertiary, quaternary, etc. alloys are disclosed. Specific examples are given to a Pd.sub.77.5 Cu.sub.6 Si.sub.16.5 alloy and a Ni.sub.40 Pd.sub.40 P.sub.20 alloy. The patent also discloses ternary alloys of the formula M.sub.a Y.sub.b Z.sub.c in sheet, ribbon and powder form wherein M is Fe, Ni, Cr, Co or V, Y is P, C or B and Z is Al, Si, Sn, Sb, Ge, In or Be.
As can be appreciated, the disclosure of the foregoing patent does not teach the alloys of this invention nor does it indicate that any advantages occur in a silver-copper-indium system. Furthermore, it teaches that in order to be ductile the alloy must contain at least 50 percent amorphous phase.
It is believed, therefore, that a silver-copper-indium alloy in the form of a thin brazing foil that can contain up to 18 atomic percent of indium is an advancement in the art.